Ever since the release of certain versions of Firefox, I haven't been able to use the feature and didn't know why. Originally I had asked on the IPS forums on how to fix this error and got some responses which were not helpful. You can check out the thread here.
In any case, if you were wondering how to regain this functionality, here are the steps you need to take:
- about:config
- search for "ui"
- Change ui.key.chromeAccess to 5
- Change ui.key.contentAccess to 4
Hope this helps . Maybe I've even showed you a feature of the board which you didn't know about before .